[Taxacom] Forgotting at the edge of miracles

John Grehan calabar.john at gmail.com
Sun Apr 26 11:08:53 CDT 2015


Thanks for the clarification. I am travelling for a week and may have only
intermittent email contact, so will respond/comment in due course.

John Grehan

On Sun, Apr 26, 2015 at 11:07 AM, Richard Pyle <deepreef at bishopmuseum.org>

> > Could you put a bit of meat on your characterization?
> A bit?  Sure.
> > What do you mean by a single 'model' that accounts for all distributions.
> Well, we have lots of proposed hypotheses about historical mechanisms to
> account for modern geographic distribution patterns of organisms.  Some
> (most?) of these hypotheses involve mechanisms that occur on evolutionary
> time scales (i.e., the implication being that present-day patterns of
> geographic occurrence of organisms reflects historical patterns of
> geographic speciation of organisms). Other hypotheses involve mechanisms
> that occur on ecological (i.e., sub-evolutionary) time-scales (the
> implication being that present-day patterns of geographic occurrence does
> not necessarily reflect historical patterns of speciation).  Good
> hypotheses show how existing evidence "fits" the proposed mechanism behind
> how populations of organisms got to be where they are now. Better
> hypotheses show how the existing evidence "fits" the proposed mechanism
> behind how populations of organisms got to be where they are now MORE
> EFFECTIVELY than alternative hypotheses (i.e., in many cases, the same
> evidence often "fits" multiple different competing hypotheses).  The BEST
> hypotheses make specific, testable predictions about future (but not yet
> acquired) evidence, in ways that support one hypothesis over others.
> This is all good -- exactly the sort of process by which science SHOULD
> progress (i.e., using empirical data to support or refute alternate
> competing hypotheses).
> Now, getting to your question, I used the word "model" as a more inclusive
> term of "mechanisms".  So, one "model" of biogeography, for example, is
> that organisms occur where they do now because historical vicariant events
> have shaped patterns of allopatry and subsequent speciation.  Another model
> of biogeography is that organisms occur where they do now because
> historical dispersal of organisms has shaped patterns of allopatry and
> subsequent speciation.  Other models involve mechanisms of extinction and
> re-colonization, or consequences of both organism-induced and Earth-induced
> factors, or various other sets of factors.
> I was echoing and extending Tony's complaint of "A presumption of
> dispersal as an explanation for everything makes for uninteresting, and
> ultimately irrelevant, research",  to replace the word "dispersal" with
> *any* mechanism that has been proposed to account for modern geographic
> distribution patterns of organisms; the key phrase being "as an explanation
> for everything".
> The point I was trying to make is that often-times combatants in these
> biogeopgraphic debates act as though there is necessarily one dominant
> mechanism to explain modern distribution patterns of most organisms, and
> the alternate mechanisms only apply to exceptional situations.  Maybe
> different mechanisms play greater or lesser roles for different kinds of
> organisms (e.g., coral-reef fishes vs. terrestrial mammals). Maybe in some
> cases, modern distribution patterns correlate well with historical patterns
> of speciation. Maybe in other cases, they don't.  My main point is that the
> word "Maybe" applies here because we are still "SO, SO, SO far away from
> understanding both evolutionary history and the actual distribution
> patterns of most living things".
> > And what is the basis for your contention that we are 'SO, SO' far away
> from understanding evolutionary history and distributions of living things.
> That's easy:
> 1) The most plausible estimates put total diversity at around 10-30
> million species. We've only cataloged about 2 million (let's call it 10%).
> We obviously don't know the distribution patterns of species that we don't
> even know exist yet. So, at BEST, the evidence to support alternative
> mechanisms behind patterns of speciation and biogeography are using only
> 10% of available evidence.
> 2) We are, of course, far from the "BEST" situation (i.e., 10%) because we
> have not yet confidently established evolutionary relationships among the
> 10% of organisms we do know about. For example, molecular evidence strongly
> supports a phylogeny of ((Humans, Chimps), Orangutans); yet you have shared
> with this list in the past compelling morphological and other non-molecular
> evidence to support a phylogeny of ((Humans, Orangutans), Chimps).  If the
> best we can say about one of the most well-studied examples of evolutionary
> relationships is, "we have conflicting evidence"; then where does that
> leave us with the rest of the 2 million species?
> 3) Even if we ignore our ignorance of evolutionary relationships, and
> simply trust our assessment of species boundaries to focus on inferring
> mechanisms of biogeography from observed distribution patterns (without
> trying to correlate to patterns of speciation), we are still woefully
> lacking in our documentation of the current distribution patterns of most
> of the known species (let alone the unknown species).
> > Who in biogeography has made claims that we are close to fully
> understanding it
> Well, we have these seemingly endless (and sometimes fierce) arguments
> about biogeography, and historical mechanisms to explain observed modern
> patterns of distribution. What are these arguments about, if not,
> fundamentally "Mechanism 'X' explains most distribution patterns better
> than mechanism 'Y'"?  My point (again, to echo Tony's), is that such strong
> convictions about historical mechanisms behind apparent modern distribution
> patterns of organisms (and especially when those patterns are correlated
> with inferred patterns of speciation) are wholly unwarranted when they are
> based on largely incomplete knowledge of current distribution patterns and
> evolutionary relationships of something like 10% of biota.
> I hope that addresses your questions.
> Aloha,
> Rich

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